The present invention relates to the general field of rapid prototyping technology, and in particular, to stereolithography methods and systems.
Rapid prototyping (RP) technologies, also known as Solid Freeform Fabrication (SFF), layered manufacturing and other similar technologies enable the manufacture of complex three-dimensional (3D) parts. RP technologies, in particular, generally construct parts by building one layer at a time. RP technologies are commonly used to build parts and prototypes for use in, for example, the toy, automotive, aircraft and medical industries. Oftentimes prototypes made by RP technologies aid in research and development and provide a low cost alternative to traditional prototyping. In a few cases, RP technologies have been used in medical applications such as those associated with reconstructive surgery and tissue engineering (TE).
Stereolithography (SL) is one of the most widely used RP technologies known in the art. The resolution of SL machines and the ability of SL to manufacture highly complex 3D objects, make SL ideal for building both functional and non-functional prototypes. In particular, SL techniques provide an economical, physical model of objects quickly and prior to making more expensive finished parts. The models are readily customizable and changes may be easily implemented.
SL generally involves a multi-stage process. For example, the first stage involves designing and inputting a precise mathematical geometric description of the desired structure's shape into one of many computer-aided design (CAD) programs and saving the description in the standard transform language (STL) file format. In the second stage, the STL file is imported into SL machine-specific software (RP software). The RP software slices the design into layers and determines the placement of support structures to hold each cross-section in place while building the structure layer by layer. By computing build parameters, the RP software controls the part's fabrication. In the layer preparation stage, the build parameters for the desired part are translated into machine language. Finally, the machine language controls the SL machine to build a desired part and its support structure layer by layer. SL machines typically focus an ultraviolet (UV) laser onto a cross-section of a liquid photopolymer resin. The laser, in turn, selectively cures a resin to form a structure, such as anatomical shapes (i.e., organs and tissues), layer by layer. Ultimately, the part is cleaned, the support structure is removed and the part is post-cured (typically exposed to UV) prior to completion.
SL technologies known in the art generally include, for example, a laser, a liquid level sensing system, laser beam optics and controllable mirror system, a vertically movable platform, single resin retaining receptacle or vat and a recoating device. During the laser scanning phase, a series of optics and controllable mirrors raster a UV laser beam to solidify a photocurable polymer resin. The subject 3D part is first attached to the platform by building a support structure with the platform in its topmost position. This step allows for misalignment between the platform and the surface of the liquid resin—once constructed, the base support structure is parallel with the surface of the liquid. When building the subject part simultaneously with its required support structure and after the laser beam completes a layer, the platform typically is vertically traversed downward a distance equal to the build layer thickness. After the platform is vertically traversed downward and prior to selectively curing the next layer, a recoating device is typically traversed horizontally across the part that deposits a uniform layer of liquid polymer across the part. The recoating device ensures that trapped spaces within the part are filled with liquid resin (which may be required for future build layers), and is used to maintain a constant build layer thickness. The process repeats as each layer is built. Complex-shaped parts are thus manufactured by repeating the layering process. Once complete, the part is typically raised out of the liquid polymer, the support structure is removed from the part and the part is cleaned and then post-cured. The operator may, however, need to sand, file or use some other finishing technique on the part in order to provide a specific surface finish to the structure, which may include painting, plating and/or coating the surface.
TE techniques, in particular, rely on necessary fluids, growth factors and cells to perfuse through the pores of a scaffold (a supporting structural and potentially bioactive framework used in tissue engineering for directed cell growth). One of the most challenging problems in TE involves promoting cell in-growth and perfusion to seeded cells in implanted scaffolds. The diffusion of oxygen and nutrients is not sufficient to sustain cell viability beyond distances of approximately 100 microns in the body. TE techniques, therefore, must retain precise control over the resulting 3D geometry to design favorable perfusion into a scaffold thus maintaining cell viability. SL technologies allow direct manufacturing of perfusion promoting implantable scaffolds. Hydrogels are biocompatible materials that exhibit favorable perfusion characteristics and are currently used in photolithographic processes using manual lithographic masking techniques as well as a variety of other processes. Implantable multi-material hydrogel constructs, however, are not currently suited for single material SL machines known in the art.
Accordingly, improvements in part building technology are desired. Specifically, there is a need for a low cost, efficient and easy to use stereolithography system that accommodates multiple building materials or resins. What is desired is a system that maintains a non-contaminating and sterile building environment while accommodating intermediate cleaning and curing between materials and/or resins. For example, when building biomedical implantable structures and/or devices, it is imperative to maintain a sterile building environment. It is equally important that resin or resin residue from one portion of the build does not contaminate any other resin when building with multiple materials, and thus, intermediate washing between materials is a critical element of the desired system. What is also desired is a multiple resin system to directly manufacture complex multiple-material, functional and non-functional prototypes and finished devices. What is further desired is an SL system that accommodates building multiple material, implantable hydrogel structures and other microstructures. What is still further desired is an SL system that allows additives, such as color (pigments, dyes and other color additives known in the art), to incorporate into resins on a layer by layer basis. Still another desire is to have a system that allows other resin additives and/or other materials (as in part embedding or cell seeding) to alter characteristics, such as the strength, mechanical, optical, thermal, electrical, functional and biofunctional properties of the resin and/or resulting model on a layer by layer basis or even within a single layer.